Fluid servo-motors



$125 26, 1955 F. J. BRADBURY ET AL V FLUID SERVO-MOTORS 4 Sheets-Sheet 1 Filed Feb. 20, 1953 Juiy 26, 1955 F. J. BRADBURY ET AL 2,713,850

FLUID SERVO-MOTORS Filed Feb. 20, 1953 4 Sheets-Sheet 2 FLUID SERVO-MOTORS 4- Sheets-Sheet 3 Filed Feb. 20, 1955- J [Ill/[11117 July 26, 1955 F. J. BRADBURY ET AL 2,7 3,8 0

FLUID SERVO-MOTORS 4 Sheets-Sheet 4 Filed Feb. 20 1955 nite FLUID SERVO-MOTORS Application February 20, 1953, Serial No. 338,086

9 Claims. (Cl. 121-38) This invention relates to fluid operated servo-motors, of either the fluid pressure or the vacuum type, for efiecting operations such as the disengagement of friction clutches which are engaged by spring loading. Servo-motors for such purposes are single acting, the return movement being effected by the spring means of the clutch of other controlled device. The object of the present invention is to provide a single-acting servo-motor, which, on its return stroke provides a rate of movement which is reduced automatically When the load falls below a predetermined limit. Such a servo-motor enables a clutch to take up the drive smoothly, provided that there is some degree of resilience in the engaging members, since initial engagement relieves the servo-motor of a proportion of the spring load.

The servo-motor may be mounted with its cylinder fixed,

and with the piston, diaphragm or equivalent connectedto the device operated by the servo-motor; alternatively the piston, diaphragm or equivalent may be fixed, and the cylinder connected to the operated device. The term movable member is used herein to define whichever part is connected to the operated device.

In a fluid operated servo-motor according to the invention a non-return valve by-passed by a restricted passage is provided in the passage through which fluid enters and leaves the working chamber of the servo-motor, said nonreturn valve'being operable by the said fluid to allow free flow thereof during the operative stroke of the servomotor and being held 011 its seat by the force developed by the servo-motor when the said force exceeds that exerted by a control spring through which the force developed by the servo-motor is transmitted.

The servo-motor may be of the vacuum-operated type, the non-return valve being opened by fluid flowing out of the working chamber, or of the pressure operated type, in which case the non-return valve is opened by fluid flowing into the working chamber.

The invention is hereinafter described with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic view showing one form of vacuum servo-motor according to the invention arranged for operating a friction clutch of the single plate type;

Figure 2 is a sectional elevation of the servo-motor shown in Figure 1;

Figure 3 is a sectional elevation, similar to Figure 2, of a modified arrangement according to the invention; and

Figure 4 is a view similar to Figures 2 and 3, but showing a pressure operated servo-motor.

Referring to Figure 1 of the drawings, the engine of a vehicle is indicated at 10, and the bell housing enclosing the clutch at 11. The clutch itself is generally indicated by the reference 12, and includes a driven plate 13 mounted on splines on the input shaft (not shown) of a gearbox through which the drive is transmitted to the vehicle wheels, a pressure plate 14 urged by springs 15 to clamp the driven plate 13 against a flywheel 16 mounted on the engine crankshaft, and a cover plate 17, bolted to the flywheel, providing an abutment for the springs 15. The driven plate 13 has two facings of friction material tates Patent r sufiicient to'overcome the spring 52, however, the valve- 18 mounted one on each side thereof and having interposed between them cushion members 19 consisting of bowed or crimped segments of spring metal secured to the edge of a supporting plate (not shown). The pressure plate 14 is moved away from the flywheel 16 by release levers, one of which is shown at 22, being pivotally mounted intermediate its ends on a bracket 23 carried by the cover plate 17, and engaging at its outer end with an undercut lug 24 on the pressure plate. A release bearing 25 engages the inner ends of the release levers 22, and

is moved to release the clutch by a throw-out fork 26.

pivotally mounted in the bell-housing 11 at 27. A lever arm 28 integral with the throw-out fork 26 projects from the bell-housing.

The cylinder 29 of a vacuum servo-motor 31 is fixed in a convenient position to the vehicle structure, and to a diaphragm 32 constituting the movable member of the servo-motor is secured a sleeve 33 in which is mounted for limited longitudinal movement, a tube 34. A fitting 35 on the outer end of the tube 34 provides a connection thereto for a pull rod 36, the other end of which is pivotally connected to the arm 28, and also a connection for a conduit 37 leading to a two-way valve 38 by means of which the conduit 37 can be placed in communication witheither a conduit 39 leading to the inlet manifold 41 of the engine 10, or with an air inlet 43.

The servo-motor 31 is shown in greater detail in Figure 2, reference to which will show that the centre of the diaphragm 32 is clamped between two rigid discs 44 and 45, and the sleeve 33 is screwed into an end member 46 passing through aligned apertures in the said discs and secured in position by a nut 47. The bore of the sleeve 33 is enlarged adjacent the end member 46 to provide a valve chamber 48, and the tube 34 is guided in a bearing 49 screwed into the outer end of the sleeve 33 and secured by a locknut 51. A spring 52 taking its abutment on the inner end of the bearing 49 acts on a flange 53 on the tube 34, and urges the said flange against a shoulder 54 in the sleeve 33. The inner end of the tube 34 is closed, and from it projects a stem 55 on which is slidably mounted a valve head 56 urged towards the inner end of the said stem by a light spring 57. A split pin 58 passing through the stem limits the movement of the valve head 56. A passage'59 in the end member 46 connects the valve chamber 48 with the working chamber 61 of the servo-motor, and the face of the said end member 46 bounding the inner end of the valve chamber 48 provides a seat around the said passage 59 for the valve head 56. The arrangement is such that When the flange 53 is in contact with the shoulder 54, the valve head 56 is seated, and is spaced by a small distance from the split pin 58, but outward movement of the tube 34 moves the valve head away from the face of the end member to open the passage 59. Radial ports 62 connect the interior of the tube 34 with the valve chamber 48. A restricted passage 63 is formed in the valve head 56.

The interior of the servo-motor cylinder on the opposite side of the diaphragm 32 to the working chamber 61 a is open to the atmosphere, and abutments 64 and 65, the

latter of which is adjustable, are provided to limit the stroke of the diaphragm.

When the clutch 12 is engaged, and the servo-motor is inoperative, the flange 53 on the tube is in contact with the shoulder 54 in the sleeve 33, and the valve head 56 is seated. In this position, air can flow freely out of the working chamber 61 of the servo-motor, since the valve head can move away from its seat against the spring 57, but air can enter the working chamber only at a very slow rate through the passage 63. When the sleeve 33 and tube 54 are subjected to a tension load Patented July 26, 1955 head 56 is unseated, and free flow of air can take place in both directions.

To disengage the clutch, the valve 38 is moved from the position shown in Figure l to place the conduits 37 and 39 in communication one with the other, thus applying suction to the working chamber 61 of the servomotor. The valve head 56 moves away from its seat, and a pull is applied to the pull rod 36 to disengage the clutch. During the initial stage of disengagement, when the cushion springs 19 of the clutch driven plate are expanding, the flange 53 on the tube 34 remains in contact with the shoulder 54, but when the cushion springs 19 are fully expanded, and the full load of the clutch springs 15 is supported by the servo-motor, the spring 52 yields, and the tube 34 moves relatively to the sleeve 33, the split pin 58 engaging the valve head 56 and moving it positively away from its seat.

When it is desired to re-engage the clutch, the valve 38 is returned to the position shown in Figure 1, conmeeting the working chamber 61 of the servo-motor to the atmosphere, and air enters the said chamber freely, allowing the clutch springs 15 to urge the clutch towards the engaged position. As soon as the cushion springs 19 of the driven plate begin to be compressed, however, the load on the servo-motor is reduced, and the spring 52 forces the flange 53 against the shoulder 54, thus allowing the valve head 56 to seat. The air flow is now in a direction to urge the valve head 56 towards its seat, and the passage 59 is thus closed, allowing air to enter the working chamber 61 only through the restricted passage 63, so that the final engagement of the clutch takes place at a greatly reduced rate, thus assisting in the provision of a smooth take-up of the drive.

The arrangement shown in Figure 3 of the drawings is generally similar to that shown in Figure 2, but the stem 55 is drilled axially at 66, the end of the drilling at the free end of the stern being plugged, and radial openings 7 being provided which connect with the drilling, and are so positioned that they are covered by the valve head 56 when the latter is in engagement with the split pin 58, but are exposed to the passage 59 when the valve head 56 is seated, and the flange 53 is in contact with the shoulder 54. Thus, during clutch re-engagement, the restricted passage 63 provides the sole communication with the working chamber 61 of the servo-motor only for a brief period during the extension of the spring 52, and the final engagement of the clutch takes place at a more rapid rate.

Figure 4 shows a servo-motor according to the invention which is operated by fluid under pressure. The servo-motor 68 has a diaphragm 69 constituting the movable member, the centre of the diaphragm having clamped to it, on opposite sides, two rigid discs 71, 72, which support a co-axial sleeve 73 extending slidably through an opening 74 in the end of the cylinder. A packing ring 75 provides a fluid-tight joint to prevent leakage from the working chamber 76 of the servomotor. A tube 77 slidably mounted in the sleeve 73 is connected by a pull rod, not shown, to the clutch release mechanism, a flange 78 on the tube 77 being urged by a spring 79 against a shoulder 81 in the sleeve 73. A stem 83 fixed in the sleeve 73 carries a valve head 83 adapted to seat on the end of the tube 77 under the load of a light spring 84, a split pin 85 being provided to limit the travel of the valve head. A passage 86 connects the valve chamber 37 in the sleeve 73 with the working chamber 76, and a restricted passage 88 is provided in the valve head. Fluid under pressure entering the servo-motor to release the clutch lifts the valve head 83 from its seat, and when the full clutch spring load is applied to the servo-motor the valve head is held positively away from its seat. During the return stroke of the servo-motor, the valve head 83 is unable to seat on the end of the tube 77 until the load on the pull rod is reduced by the initial engagement of the clutch, upon Cit which it seats to restrict the escape of fluid from the working chamber 76, thus reducing the rate of movement during final engagement of the clutch.

In all of the arrangements described, the seating of the valve head 56 or 83 during the return stroke of the servo-motor depends solely on the change of the load acting on the pull rod, and the point at which seating takes place is not therefore afiected by wear of the clutch facings.

The restricted passage 63 or 88 need not be formed in the valve head, but, in the case of a vacuum servo-motor, can be formed in any position where it connects the valve chamber 43 with the working chamber 61, and, in the case of a fluid pressure servo-motor, in any position where it connects the valve chamber 87 with the bore of the tube 77.

The clutch may be of the kind which includes centrifugally actuated weights acting between the pressure plate and a reaction plate on which the clutch engaging springs act, the release levers withdrawing the pressure plate, regardless of the position of the weights, by compressing the engaging springs through the reaction plate.

The servo-motor according to the invention may be used for operating the clutch in a transmission control system as described in our pending United States patent application Serial No. 271,606.

We claim:

1. A fluid operated servo-motor comprising a cylinder, a movable wall in said cylinder and defining therewith a working chamber, a force transmitting member, resilient means through which movement of the movable wall is transmitted to said force transmitting member, means defining a passage through which fluid enters and leaves said working chamber, a non-return valve in said passage openable by the working fluid during the working stroke of the servo-motor, means defining a restricted passage by-passing said non-return valve, and means operative on yielding of said resilient means to positively unseat said non-return valve.

2. A fluid operated servo-motor comprising a cylinder, a movable wall in said cylinder and defining therewith a working chamber, a force transmitting member, resilient means through which movement of the movable wall is transmitted to said force-transmitting member, means defining a passage through which fluid enters and leaves said working chamber, a non-return valve in said passage openable by suction applied to said passage to effect the working stroke of the servo-motor, means defining a restricted passage by-passing said non-return valve, and means operative on yielding of said resilient means to positively unseat said non-return valve.

3. A fluid operated servo-motor comprising a cylinder, a movable wall in said cylinder and defining therewith a working chamber, a force transmitting member, resilient means through which movement of the movable wall is transmitted to said force-transmitting member, means defining a passage through which fluid enters and leaves said working chamber, a non-return valve in said passage openable by pressure fluid admitted through said passage to effect the working stroke of said servo-motor, means defining a restricted passage by-passing said non-return valve, and means operative on yielding of said resilient means to positively unseat said non-return valve.

4. A fluid operated servo-motor comprising a cylinder,

- a movable wall in said cylinder and defining therewith a working chamber, a sleeve fixed to said movable wall and moving as one therewith, a force transmitting member slidable in said sleeve, resilient means opposing relative movement of the force transmitting member and the sleeve due to the force exerted by the servo-motor, a nonreturn valve controlling a passage in said sleeve through which fluid enters and leaves said working chamber, said non-return valve being openable by the working fluid during the working stroke of the servo-motor, means defining a restricted passage by-passing said non-return valve, and means on said force transmitting member to engage said non-return valve and open it when the resilient means yields.

5. A fluid operated servo-motor according to claim 4, wherein the force transmitting member comprises a tube through which the working fluid passes.

6. A fluid operated servo-motor comprising a cylinder, a movable wall in said cylinder and defining therewith a working chamber, a sleeve fixed to said movable Wall and moving as one therewith, a tubular force transmitting member slidable in said sleeve, abutments on said sleeve and on said force-transmitting member, a spring between said abutments through which tensional force exerted by said servo-motor is transmitted to said force transmitting member, said sleeve and force-transmitting member constituting a passage through which fluid enters and leaves the Working chamber, non-return valve means in said passage comprising a valve seating in said sleeve and a valve member co-operating with said seating, a restricted passage by-passing said non-return valve, a stem on said force-transmitting member on which said valve member is slidably mounted, and means on said stem limiting the sliding movement of the valve member thereon, relative movement of said sleeve and said force-transmitting member when said spring yields causing movement of said valve member away from its seat.

7. A fluid operated servo-motor according to claim 6, wherein a second by-pass for the non-return valve means is provided, said second by-pass comprising passage means in the stem and lateral ports communicating with said passage means, said lateral ports being obturated by the valve member when the latter is unseated by relative movement of the sleeve and the force-transmitting memher.

8. A fluid operated servo-motor comprising a cylinder, a movable wall in said cylinder and defining therewith a working chamber to receive pressure fluid for operating the servo-motor, a sleeve fixed to said movable wall and moving as one therewith, a tubular force-transmitting member slidable in said sleeve, abutments on said sleeve and on said force-transmitting member, a spring between said abutments through which tensional force exerted by the servo-motor is transmitted to said force-transmitting member, said sleeve and forcetransmitting member constituting a passage through which fluid enters and leaves the working chamber, non-return valve means in said passage comprising a valve seating on said forcetransmitting member and a valve member cooperating with said seating, a restricted passage by-passing said non-return valve, a stem carried by said movable wall on which said valve member is siidably mounted, and means on said stem limiting the sliding movement of the valve member thereon, relative movement of said sleeve and said torce-transmitting member when said spring yields causing movement of said valve member away from its seat.

9. A vacuum servo-motor comprising two casing mem bers defining a cylinder, a diaphragm clamped between said casing members and defining with one of said members a working chamber, a sleeve fixed to said diaphragm and moving as one therewith, a tubular force-transmitting member slidable in said sleeve, abutments on said sleeve and on said force-transmitting member, a spring between aid abutments through which tensional force exerted by aid servo-motor is transmitted to said force-transmitting member, said sleeve and force-transmitting member constituting a passage through which fluid enters and leaves the working chamber, nonreturn vaive means in said passage comprising a valve seating in said sleeve and a valve member cooperating with said seating, a restricted passage by-passing said non-return valve, a stem on said force-transmitting member on which said valve member is slidably mounted, and means on said stem limiting the sliding movement of the valve member thereon, relative movement of said sleeve and said force-transmitting member when said spring yields causing movement er" said valve member away from its seat.

References Cited in the file of this patent UNITED STATES PATENTS 917,642 McElroy Apr. 6, 1909 1,283,179 Hennebohle Oct. 29, 1918 FOREIGN PATENTS 290,099 Germany Sept. 12, 1916 

